1. Field of the Invention
The present invention relates to an A-D converter, an A-D convert method, and an A-D convert program. More particularly, the present invention relates to an A-D converter, an A-D convert method, and an A-D convert program for outputting a digital output signal obtained by digitalizing an analog input signal.
2. Related Art
An A-D converter converts an analog signal into a digital signal. The A-D converter is classified into a single bit mode quantizing bits by one bit with one clock and a multiple bit mode quantizing bits by multiple bits with one clock. The A-D converter with a single bit mode includes, for example, a successive comparison A-D converter and a ΔΣ type A-D converter. The successive comparison A-D converter is disclosed in Ricardo E. Suarez, Paul R. Gray, and David A. Hodges, “An All-MOS Charge-Redistribution A/D Conversion Technique”, IEEE International Solid-State Circuits Conference, 1974, P. 194-195 and 248, James McCreary and Paul R. Gray, “A High-Speed All-MOS Successive-Approximation Weighted Capacitor A/D Conversion Technique”, IEEE International Solid-State Circuits Conference, 1975, P. 38-39 and 211, JAMES L. McCREARY and PAUL R. GRAY, “All-MOS Charge Redistribution Analog-to-Digital Conversion Techniques-Part 1”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-10, NO. 6, DECEMBER 1975, P. 371-379. The A-D converter with a multiple bit mode includes, for example, a flash type A-D converter.
Meanwhile, the A-D converter with a multiple bit mode has a short conversion time compared to the A-D converter with a single bit mode. However, in case of the A-D converter with a multiple bit mode, its circuit scale becomes large when realizing high resolution. On the other hand, the A-D converter with a single bit mode has a small circuit scale compared to the A-D converter with a multiple bit mode. However, in case of the A-D converter with a single bit mode, its conversion time gets longer because bits are converted by one bit when realizing certain resolution.
Furthermore, in case of the A-D converter with a multiple bit mode and the A-D converter with a single bit mode, precision becomes bad because a quantization width becomes narrow and likelihood for noises decreases when realizing high resolution. When an input signal is amplified by an operational amplifier in order to solve this, the A-D converters with a multiple bit mode and a single bit mode have increased power consumption and further their precision is dependent on a characteristic of the operational amplifier.